Recently, U.S. Pat. No. 4,375,516 disclosed phosphate ceramic materials which could be prepared in rigid form from a composition comprising a metal oxide, calcium silicate and phosphoric acid. As disclosed therein, the resulting products could be used in a variety of building products.
In view of their potential uses, various procedures were used to provide building products having decorative finishes, examples of which are embossing techniques and color printing techniques; nevertheless, such decorative features are not satisfactory in all circumstances. Accordingly, it was desired to find a process by which selected portions of a phosphate ceramic surface could be provided with open celled areas which provided an enhanced, three-dimensional appearance.
One approach by which this effect may be achieved is by selectively treating certain portions of the surface of an uncured composition with a basic material. The base reacts with the phosphoric acid present in the initial composition to yield open cells; however, because the base must react with the acid, the base must be applied at a point in time before the board is cured; i.e., before the acid is neutralized by the curing process. For a number of reasons, this is not a particularly satisfactory approach.
Accordingly, one objective of the present invention was to provide a simple means by which a portion of a phosphate ceramic surface could be provided with an open-celled, three-dimensional character.
A second object of the present invention was to provide a method by which such features could be provided to the board on a continuous basis without the necessity of utilizing an acid-base reaction.
These and other objectives of the present invention will become apparent from the detailed description of preferred embodiments which follows.